The primary goal of this proposal is to gather more information concerning the functional and anatomical properties of primary afferent neurons in the trigeminal system that underlie mandibular kinesthesia. Anatomical (Romfh et al., 1979) and microelectrode studies (Capra et al., 1978; Lund and Matthews, 1979) show that temporomandibular joint (TMJ) afferents, cutaneous mechonoreceptors and certain masticatory muscle afferents are responsive to jaw movements and are innervated by cells with perikarya located in the caudal portion of the trigeminal ganglion. Periodontal afferents and muscle spindle afferents innervated by cells of the mesencephalic nucleus may also be involved in certain aspects of kinesthetic perception (Anderson and Matthews, 175; Capra, 1981). The relative contribution from various peripheral receptors to the conscious appreciation of mandibular position is incompletely understood. Preliminary results in our laboratory indicate that single nerve fibers branch to innervate both TMJ receptors and cutaneous mechanoreceptors. Branching of peripheral fibers would allow early integration of neural information related to jaw movement. The convergence of first order kinesthetic signals in the brain stem trigeminal nuclei similar to that observed in spinal systems (Millar, 1979) also merits further investigation. Neurons responsive to precise jaw movements will be identified in the trigeminal ganglion and in brain stem trigeminal nuclei with extracellular mocroelectrodes. Attempts to identify the specific structures innervated by each unit will be made by electrical stimulation, adequate natural stimulation, antidromic activation and collision testing. Latency of response, conduction velocity, and the pattern of firing related to the extent and rate of specific jaw movements wll be determined for each unit. Routine histological studies and horseradish peroxidase (HRP) studies will be performed to determine the structural properties and specific somatotopic localization of cells that innervate the TMJ and muscles of mastication. Anatomical and physiological data will be correlated in order to develop and refine models of neuronal circuits that are operative in the mediation of mandibular position sense.